Toluenes oxidation

The cumene oxidation route is the lea ding commercial process of synthetic phenol production, accounting for more than 95% of phenol produced in the world. The remainder of synthetic phenol is produced by the toluene oxidation route via benzoic acid. Other processes including benzene via cyclohexane, benzene sulfonation, benzene chlorination, and benzene oxychl orin ation have also been used in the manufacture of phenol. A Hst of U.S. phenol production plants and their estimated capacities in 1994 are shown in Table 2, and worldwide plants and capacities are shown in Table 3. 

Conversion per pass is reported to be low, 10—20%, with equally low yields, 30—50% (5). The vapor-phase oxidation of toluene was the dominant toluene oxidation process ia the 1950s and early 1960s, but is no longer of iadustrial importance. The Hquid-phase process now dominates. 

In the United States all other processes have been completely phased out and virtually all benzoic acid is manufactured by the continuous hquid-phase air oxidation of toluene. In the late 1950s and the early 1960s both Dow Chemical and Snia Viscosa constmcted faciUties for Hquid-phase toluene oxidation because of large requirements for benzoic acid in the production of phenol and caprolactam. Benzoic acid, its salts, and esters are very useful and find appHcation in medicinals, food and industrial preservatives, cosmetics, resins, plasticizers, dyestuffs, and fibers. 

Figure 10-14. The SNIA BPD process for producing caprolactam (1) toluene oxidation reactor, (2) fractionator, (3) hydrogenation reactor (stirred autoclave), (4) multistage reactor (conversion to caprolactam), (5) water dilution, (6) crystallizer, (7) solvent extraction, (8) fractionator.

Phenol is the starting material for numerous intermediates and finished products. About 90% of the worldwide production of phenol is by Hock process (cumene oxidation process) and the rest by toluene oxidation process. Both the commercial processes for phenol production are multi step processes and thereby inherently unclean [1]. Therefore, there is need for a cleaner production method for phenol, which is economically and environmentally viable. There is great interest amongst researchers to develop a new method for the synthesis of phenol in a one step process [2]. Activated carbon materials, which have large surface areas, have been used as adsorbents, catalysts and catalyst supports [3,4], Activated carbons also have favorable hydrophobicity/ hydrophilicity, which make them suitable for the benzene hydroxylation. Transition metals have been widely used as catalytically active materials for the oxidation/hydroxylation of various aromatic compounds. 

McClay K, SH Streger, RJ Steffan (1995) Induction of toluene oxidation in Pseudomonas mendocina KRl and Pseudomonas sp. strain ENVPC5 by chlorinated solvents and alkanes. Appl Environ Microbiol 61 3479-3481. 

Leahy JG, AM Byrne, RH Olsen (1996) Comparison of factors influencing trichloroethylene degradation by toluene-oxidizing bacteria. Appl Environ Microbiol 62 825-833. 

Altenschmidt U, G Fuchs (1992) Anaerobic toluene oxidation to benzylalcohol and benzaldehyde in a denitrifying Pseudomonas sp. J Bacteriol 174 4860-4862. 

The oxidation of toluene to benzaldehyde and benzoic add over V205/Ti02 assisted by microwaves was studied by Liu et al. [82]. The authors conduded that microwave energy can greatly improve the process of selective toluene oxidation. The highest yields of benzoic add were, however, only 38—41% and the highest selectivity was 51% at 80% conversion to benzoic add. 

Phenol has been obtained by distillation from petroleum and synthesis by oxidation of cumene or toluene, and by vapor-phase hydrolysis of chlorobenzene (USITC 1987). In 1995, 95% of U.S. phenol production was based on oxidation of cumene except at one company that used toluene oxidation and a few companies that distilled phenol from petroleum (CMR 1996). In 1995 the total annual capacity of phenol production approached 4.5 billion pounds (CMR 1996). 

FIGURE 3.14 Molar rates of progress for toluene oxidation in an atmospheric turbulent flow reactor (c/. to Fig 3.13). The benzene submechanism is outlined for toluene oxidation. Dashed arrows represent paths that are important to benzene oxidation, but not significant for toluene (from Ref. [66]). 

Phenol (508) is found to be produced continuously from benzene (507) by aerial oxidation in aqueous sulfuric acid when a Cu(I)/Cu(II) redox couple is used as a mediator (Scheme 176) [581]. The Cu(I)-mediated electroreduction of oxygen in the presence of chloride is found to be effective for toluene oxidation, leading to benzaldehyde and benzyl chloride [582]. Recently, benzene has also been oxidized... 

Ibusuki, T. and Takeuchi, K. Toluene oxidation on U.V.-irradiated titanium dioxide with and without O2. NO2 or H2O at ambient temperature, Atmos. Environ., 29(9) 1711-1715, 1986. 

A third problem is related to the slow baek-desorption of the produets of reaetion, when they form on metal-oxide nanopartieles within a host ordered porous siliea matrix. For example, in toluene oxidation to benzaldehyde over Fe-Mo-oxide nanopartieles stabilized within a siliealite matrix, the slow rate of reoxidation of the redueed Fe-Mo-oxide, due to the low nanopartiele size, inereases the presenee of redueed molybdenum sites, whieh, interaeting with the earbonyl group of benzaldehyde, slow down the desorption and enhanee the rate of the eonseeutive oxidation. " ... 

Species such as cresol are known to be products of the toluene oxidation and have commonly been assumed to be formed via reactions such as (63)... 

Such a reaction mechanism could initiate toluene oxidation and increase the observed removal rates and overall conversion of the toluene. 

Alternatively, some of the reaction intermediates generated during the photocatalytic oxidation of aromatic contaminants may be rather recalcitrant to chlorine radicals, leading to the apparent deactivation phenomenon. Thermodynamically, intermediate species that are recalcitrant toward hydroxyl radicals may be recalcitrant toward chlorine radicals as well (Table 3). The accumulation of these recalcitrant reaction intermediates on the catalyst surface may gradually reduce the effectiveness of chlorine radicals in the photocatalytic system, decreasing the chlorine-promoted enhancement in toluene oxidation to negligible levels [51]. 

You have a 10 m3 bioreactor containing a diverse mixture of bacteria. It is fed at 2 m3 d-1 with a waste water containing 100 /tM toluene (for structure see P 17.1). The waste water also contains a complex mixture of nontoxic organic chemicals. Due to the biodegradation of all the substances in the waste, the steady-state 02 concentration in the reactor is only 3 /tM. If the toluene oxidizers in the tank exhibit the properties shown below, what will the steady-state toluene concentration QtM) be exiting the tank How would this result change if 02 could be added to maintain a 30 /tM steady-state concentration of 02 in the reactor ... 

Reaction. Typical liquid-phase toluene oxidizer reaction conditions may be as follows ... 

The recovery and purification of benzoic acid from a liquid-phase toluene oxidizer may involve distillation alone or it may involve a combination of distillation followed by extraction and crystallization. 

In either case, the initial distillation involves separating toluene and any material lower boiling than benzoic acid and recycling those low boilers to the toluene oxidizer. The benzoic acid and higher boiling fractions are then distilled and/or subjected to an extraction and crystallization process to... 

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